ABSTRACT: A cochlear-implant (CI) restores high levels of speech understanding to individuals across the lifespan. However, a gap in knowledge exists because we do not understand how aging affects hearing in CI users. Aging is associated with changes at multiple levels of the brain, thereby making it difficult to determine if the poorer auditory performance that occurs with advancing age is a result of changes in the auditory periph- ery, central auditory neural structures, cognition, or a combination of the three mechanisms. Since a CI by- passes the cochlea, we propose an innovative approach for investigating aging and hearing by using a human CI model. Using age (younger vs older adults) and group (CI vs normal hearing, NH) comparisons will allow us to determine the age-related contributions of cochlear and central factors to hearing. The long-term goals of this project are to (1) determine how to maximally remediate age-related auditory and cognitive processing def- icits with a CI and (2) better understand the biological effects of auditory aging. The objective of this grant is to establish age as an observable and significant factor for auditory temporal processing in CI users. Our central hypothesis is that advancing age significantly degrades central temporal processing and speech understanding abilities in CI users, which is independent of the age-related peripheral hearing loss that occurs in acoustically- hearing subjects. The rationale for the proposed research is that there is a rapidly increasing number of older adults that elect to receive a CI, but there is essentially no research on this specific population that fully utilizes the available array of research tools to study hearing in this population; our field arguably has minimal direct evidence and understanding of age-related changes to auditory processing of electrical stimulation. With strong preliminary data in hand, the central hypothesis will be tested by pursuing three specific aims: (1) De- termine the extent to which temporal processing abilities decrease with age using highly-controlled and simple (non-speech) stimuli in CI subjects; (2) Determine the extent to which age-related temporal processing factors affect speech understanding in CI subjects; and (3) Determine the extent to which aging affects cortical tem- poral encoding of speech in CI subjects. This approach is innovative because: (1) the topic of aging in older CI users is an under-studied area and (2) by using a CI model, we will better understand the biological factors un- derlying how aging affects hearing. Our outcomes will provide a significant positive impact on hearing and un- derstanding speech with a CI, which will increase CI users' quality of life.